A series of studies designed to identify dietary constituents affecting cataract incidence in rats with heredity retinal dystrophy are being conducted. Various types of diets differing in ingredient composition have been evaluated. The age of onset and the incidence of cataract can be influenced by dietary changes. For instance, virtually no cataracts were observed in rats up to 12 months of age when they were fed a purified diet with casein as the protein source. When fishmeal was used instead of casein as the protein source cataracts were observed in 100% of the rats by the time they were 56 days of age. It appears that there is a correlation between the dietary calcium concentration and the cataract incidence. New studies have been initiated using purified diets with graded levels of calcium and total minerals in order to verify this correlation.